ORCID Profile
0000-0002-8466-3084
Current Organisation
University of Western Australia
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Turbulent Flows | Interdisciplinary Engineering | Plasma Physics; Fusion Plasmas; Electrical Discharges | Approximation Theory and Asymptotic Methods
Expanding Knowledge in the Physical Sciences | Expanding Knowledge in Engineering | Atmospheric Processes and Dynamics |
Publisher: AIP Publishing
Date: 03-2023
DOI: 10.1063/5.0123930
Abstract: Supernovae—explosions of stars—are a central problem in astrophysics since they contain information on the entire process of stellar evolution and nucleosynthesis. Rayleigh–Taylor (RT) and Richtmyer–Meshkov (RM) instabilities, developing during the supernova blast, lead to intense interfacial RT/RM mixing of the star's materials and couple astrophysical to atomic scales. This work analyzes some fluid dynamic mathematical aspects of the titanic task of supernova's blast. We handle mathematical challenges of RT/RM dynamics in supernova relevant conditions by directly linking the conservation laws governing RT/RM dynamics to symmetry-based momentum model, by exactly deriving the model parameters in the scale-dependent and scale-invariant regimes, and by exploring the special self-similar class for RT/RM interfacial mixing with variable accelerations. We reveal that RT/RM dynamics is strongly influenced by deterministic (the initial and the flow) conditions in the scale-dependent linear and nonlinear regimes and in the self-similar mixing regime. The theory outcomes are consistent with the observations of supernova remnants, explain the results of the scaled laboratory experiments in high energy density plasmas, and yield the design of future experiments for the accurate quantification of RT/RM dynamics in supernova relevant conditions. We find that from fluid dynamic mathematical perspectives, supernovae can be regarded as an astrophysical initial value problem. Along with the guidance of what explodes at microscopic scales, supernova remnants encapsulate information on the explosion hydrodynamics and the associated deterministic conditions at macroscopic scales. We urge such effects be considered in interpretations of the observational data.
Publisher: AIP Publishing
Date: 08-2020
DOI: 10.1063/5.0013165
Abstract: This work focuses on the long-standing problem of inertial dynamics of an interface with interfacial mass flux and reports new mechanisms for the interface stabilization and destabilization. The interface is a phase boundary separating fluids of different densities and having interfacial mass flux. To analyze the interface dynamics from a far field, we develop and apply the general matrix method to rigorously solve the boundary value problem involving the governing equations in the fluid bulk and the boundary conditions at the interface and at the outside boundaries of the domain. We find the fundamental solutions for the linearized system of equations and analyze the interplay of interface stability with flow fields’ structure by directly linking rigorous mathematical attributes to physical observables. We find that the interface is stable when the dynamics conserves the fluxes of mass, momentum, and energy the stabilization is due to an inertial mechanism causing small oscillations of the interface velocity. In the classic Landau’s dynamics, the postulate of perfect constancy of the interface velocity leads to the development of Landau–Darrieus instability. This destabilization is also linked to the imbalance of the perturbed energy at the interface. The classic Landau’s solution is found to have degeneracy lifting of the degeneracy may lead to singularity and self-similar dynamics. Our results compare well with traditional theories of combustion and propose new experiments to study the dynamics of the interface and the flow fields in combustible systems. We further conduct reactive molecular dynamics simulations to elucidate the complexity of chemical processes, to study the destabilizing effect of energy fluctuations on the interface stability, and to illustrate the chemistry-induced instabilities. In summary, we identify the extreme sensitivity of the interface dynamics to the interfacial boundary conditions, including the formal properties of fundamental solutions and the qualitative and quantitative properties of the flow fields. This provides new opportunities for studies, diagnostics, and control of multiphase flows in a broad range of processes in nature and technology.
Publisher: AIP Publishing
Date: 07-2020
DOI: 10.1063/5.0012035
Abstract: Rayleigh–Taylor instability (RTI) has critical importance for a broad range of plasma processes, from supernovae to fusion. In most instances, RTI is driven by variable acceleration, whereas the bulk of existing studies have considered only constant and impulsive acceleration. This work focuses on RTI driven by acceleration with a power-law time-dependence. We review the existing theoretical approaches, apply the group theory approach to solve this long-standing problem, and yield the unified framework for the scale-dependent dynamics of Rayleigh–Taylor (RT) bubbles and RT spikes. For the early-time linear dynamics, we provide the dependence of RTI evolution on the acceleration parameters and the initial conditions. For the late-time nonlinear dynamics, we find a continuous family of asymptotic solutions, directly link the interface velocity to the interface morphology and the interfacial shear, derive solutions for the regular bubbles and for the singular spikes, and study the stability of these solutions. The properties of special nonlinear solutions in the RT family are scrupulously described, including the critical, Taylor, Layzer-drag, and Atwood solutions. It is shown that the fastest Atwood bubble is regular and stable, and the fastest Atwood spike is singular and unstable. The essentially multi-scale and interfacial character of RT dynamics is demonstrated. The former can be understood by viewing the RT coherent structure of bubbles and spikes as a standing wave with the growing litude. The latter implies that RT flow has effectively no motion of the fluids away from the interface and has intense motion of the fluids near the interface, with shear-driven vortical structures appearing at the interface. Our theory agrees with available observations and elaborates extensive benchmarks for future research and for better understanding of RT driven phenomena in plasmas.
Publisher: AIP Publishing
Date: 04-2021
DOI: 10.1063/5.0040842
Abstract: Unstable interfaces are omnipresent in plasma processes in nature and technology at astrophysical and at molecular scales. This work investigates the interface dynamics with interfacial mass flux and focuses on the interplay of macroscopic and microscopic stabilization mechanisms, due to the inertial effect and the surface tension, respectively, with the destabilizing acceleration. We derive solutions for the interfacial dynamics conserving mass, momentum, and energy and find the critical values of the acceleration, density ratio, and surface tension separating the stable and unstable regimes. While the surface tension influences only the interface, its presence leads to the formation of vortical structures in the bulk. The vortical structures are energetic in nature, and the velocity field is shear free at the interface. We find that the conservative dynamics is unstable only when it is accelerated and when the acceleration value exceeds a threshold combining the contributions of macroscopic and microscopic mechanisms. In the unstable regime, the interface dynamics corresponds to the standing wave with the growing litude and has the growing interface velocity. For strong accelerations and weak surface tensions typical for high energy density plasmas, the unstable conservative dynamics is the fastest when compared to other instabilities it has finite values of the initial perturbation wavelength at which the interface is stabilized and at which its growth is the fastest. We elaborate extensive theory benchmarks for experiments and simulations and outline its outcomes for application problems in nature and technology.
Publisher: AIP Publishing
Date: 06-2020
DOI: 10.1063/1.5140488
Abstract: Richtmyer–Meshkov instability (RMI) plays an important role in many areas of science and engineering, from supernovae and fusion to scramjets and nano-fabrication. Classical RMI is induced by a steady shock and impulsive acceleration, whereas in realistic environments, the acceleration is usually variable. We focus on RMI induced by acceleration with power-law time-dependence and apply group theory to study the dynamics of regular bubbles. For early time linear dynamics, we find the dependence of the growth rate on the initial conditions and show that it is independent of the acceleration parameters. For late-time nonlinear dynamics, we consider regular asymptotic solutions, find a continuous family of such solutions, including their curvature, velocity, Fourier litudes, and interfacial shear, and study their stability. For each solution, the interface dynamics is directly linked to the interfacial shear. The non-equilibrium velocity field has intense fluid motion near the interface and effectively no motion in the bulk. The quasi-invariance of the fastest stable solution suggests that the dynamics of nonlinear RM bubbles is characterized by two macroscopic length scales: the wavelength and the litude, in agreement with observations. The properties of a number of special solutions are outlined. These are the flat Atwood bubble, the curved Taylor bubble, the minimum shear bubble, the convergence limit bubble, and the critical bubble. We elaborate new theory benchmarks for future experiments and simulations.
Publisher: AIP Publishing
Date: 04-2023
DOI: 10.1063/5.0137462
Abstract: Interfacial Rayleigh–Taylor mixing is crucial to describing important natural and engineering processes, such as exploding supernovae, laser micromachining, hot spots in inertial confinement fusion, and optical telecommunications. These require the characterization of the time dependence of the driving acceleration. We compare our theoretical formulation based on group theory foundations with interface-capturing numerical simulations for linear and nonlinear two-dimensional Rayleigh–Taylor instabilities in a finite-sized domain with time-varying acceleration over broad ranges of Atwood numbers and acceleration exponents. Detailed corroboration between theory and simulations is provided for this foundational case. Both demonstrate the strong interfacial nature of Rayleigh–Taylor instabilities, which suggests that practical flow fields can be reconstructed from the derived fluid potential using the proposed theory. A robust agreement is also obtained for the early and late-time evolution of the litudes of the bubble and spike, which demonstrate that the Rayleigh–Taylor flow can transition to the mixing regime even for a single-mode initial perturbation. Corroboration with experiments of high energy density plasmas motivated by studies of supernovae is also achieved. In addition, a long-standing puzzle in Rayleigh–Taylor dynamics on the interplay between the acceleration, the shear, and the interface morphology in the theory and simulations is resolved by accounting for finite viscosity of the fluids. The characterization of Rayleigh–Taylor instabilities as a highly interfacial phenomenon provides valuable insight into its multiscale nature, which enhances the design and understanding of numerous processes of practical interest.
Publisher: AIP Publishing
Date: 12-2022
DOI: 10.1063/5.0120521
Abstract: Rayleigh–Taylor (RT) interfacial mixing is critically important in a broad range of processes in nature and technology. To understand self-similar RT dynamics, a bias free interpretation of data is in need. This work yields the physics properties and the anomalous scaling of Rayleigh–Taylor mixing based on the analysis of experimental data. Fluctuations spectra are analyzed of the specific kinetic energy of the velocity component in the acceleration direction, the density, and the mass flux. Theoretical foundations and statistical method are developed, under group theory guidance, to investigate unprocessed data, and identify with statistical confidence their spectral shapes. These include the mean values of the spectral shape's parameters, their relative errors, and the goodness of fit. The Anderson–Darling test is employed to inspect the residuals. The intervals of mode numbers are found, where the relative errors of the spectral shape parameters are small and the goodness of fit is excellent. We reveal that spectral shapes of fluctuations in RT mixing experiments can be well described by compound functions, represented by a product of a power law and an exponential. The data analysis based properties unambiguously identifies the dynamic specificity and heterogeneity of RT mixing.
Publisher: AIP Publishing
Date: 05-2021
DOI: 10.1063/5.0040880
Abstract: An exploding water plasma experiment at UCLA investigated the expansion and morphology of a fireball with and without an external magnetic field. Diagnostics include photographs and movies (which may be downloaded) acquired with a framing camera, magnetic probes, and visible light spectra. The expansion and internal magnetic fields are very different from the unmagnetized case when a magnetic field of order 300G is applied along the expansion axis. Visible light spectra are brighter and additional lines are seen in the presence of the magnetic field. The experiment can serve as a platform for studies of interfacial mixing and possibly shed light on very different processes such as laser target physics.
Publisher: AIP Publishing
Date: 12-2021
DOI: 10.1063/5.0064120
Abstract: Rayleigh–Taylor (RT) interfacial mixing has critical importance for a broad range of processes in nature and technology, from supernovas and planetary interiors to plasma fusion, oil recovery, and nano-fabrication. In most instances, RT flows are driven by variable acceleration, whereas the bulk of existing studies considered only constant and impulsive accelerations. By analyzing symmetries of RT dynamics for certain patterns of variable acceleration, we discover a special class of self-similar solutions and identify their scaling, correlations, and spectra. We find that dynamics of RT mixing can vary from superballistics to sub-diffusion depending on the acceleration and retain memory of deterministic and initial conditions for any acceleration. These rich dynamic properties considerably impact the understanding and control of Rayleigh–Taylor relevant processes in fluids, plasmas, and materials and reveal whether turbulence can be realized in RT interfacial mixing.
Publisher: AIP Publishing
Date: 04-2021
DOI: 10.1063/5.0041032
Abstract: Richtmyer–Meshkov Instability is an instability that develops at the interface between fluids of distinct acoustic impedance when impacted by a shock wave. Its applications include inertial confinement fusion, supernovae explosions, and the evolution of blast waves. We systematically study the effect of the adiabatic index of the fluids on the dynamics of strong-shock-driven flows, particularly the amount of shock energy available for interfacial mixing. Only limited information is currently available about the dynamic properties of matter at these extreme regimes. We employ smooth particle hydrodynamics simulations to ensure accurate shock capturing and interface tracking. A range of adiabatic indexes is considered, approaching limits which, to the best of the author's knowledge, have never been considered before. We analyze the effect of the adiabatic indexes on the interface speed and growth rate immediately after the shock passage. The simulation results are compared wherever possible with rigorous theories, achieving good quantitative and qualitative agreement. We find that the more challenging cases for simulations arise where the adiabatic indexes are further apart, and that the initial growth rate is a non-monotone function of the initial perturbation litude, which holds across all adiabatic indexes of the fluids considered. The applications of these findings on experiment design are discussed.
Publisher: AIP Publishing
Date: 03-2022
DOI: 10.1063/5.0088600
Abstract: Non-equilibrium transport, interfaces, and interfacial mixing play an important role in plasmas in high and low energy density regimes, at astrophysical and at atomic scales, and in nature and technology. Ex les include the instabilities and interfacial mixing in supernovae and in inertial confinement fusion, the particle-field interactions in magnetic fusion and in imploding Z-pinches, the downdrafts in stellar interiors and in the planetary magneto-convection, magnetic flux ropes and structures in the solar corona, and plasma thrusters and nano-fabrication. This Special Topic exposes the state-of-the-art research on non-equilibrium transport, interfaces, and interfacial mixing in plasmas, including theory, experiment, and simulations. The works were presented at the invited mini-conference “Non-equilibrium Transport, Interfaces and Mixing in Plasmas” at the 2019 Annual Meeting of the Division of Plasma Physics of the American Physical Society.
Publisher: Proceedings of the National Academy of Sciences
Date: 14-11-2022
Abstract: As a ubiquitous paradigm of instabilities and mixing that occur in instances as erse as supernovae, plasma fusion, oil recovery, and nanofabrication, the Rayleigh–Taylor (RT) problem is rightly regarded as important. The acceleration of the fluid medium in these instances often depends on time and space, whereas most past studies assume it to be constant or impulsive. Here, we analyze the symmetries of RT mixing for variable accelerations and obtain the scaling of correlations and spectra for classes of self-similar dynamics. RT mixing is shown to retain the memory of deterministic conditions for all accelerations, with the dynamics ranging from superballistic to subdiffusive. These results contribute to our understanding and control of the RT phenomena and reveal specific conditions under which Kolmogorov turbulence might be realized in RT mixing.
Publisher: MDPI AG
Date: 21-07-2023
Abstract: Rayleigh–Taylor (RT) interfacial mixing plays an important role in nature and technology, including atmospheric flows. In this work, we identify the physics properties of Rayleigh–Taylor mixing through the analysis of unprocessed experimental data. We consider the fluctuations spectra of the specific kinetic energy of each of the velocity components, and identify their spectral shapes, by employing the group theory guided foundations and the rigorous statistical method. We find the spectral shape parameters, including their mean values and relative errors, and apply the Anderson–Darling test to inspect the residuals and the goodness-of-fit. We scrupulously study the effect of the fitting window and identify, for each velocity component, the best fit interval, where the relative errors are small and the goodness of fit is excellent. We reveal that the fluctuations spectra in RT mixing experiments can be described by a compound function, being a product of a power-law and an exponential. The data analysis results unambiguously discovered the dynamic anisotropy and the dynamic bias of RT mixing and displayed the necessity to improve the design of experiments on RT mixing.
Publisher: American Physical Society (APS)
Date: 30-11-2020
Publisher: EDP Sciences
Date: 2023
DOI: 10.1051/MMNP/2023027
Abstract: Rayleigh-Taylor instability (RTI) is of critical important in a broad range of natural and industrial processes and is an intellectual challenge for theoretical studies. In this work, we analyze the scale-dependent linear and nonlinear Rayleigh-Taylor (RT) dynamics within the group theory approach. We link the governing equations, through an associated dynamical system based on space groups, to a momentum model based on scaling transformations. In doing so, we precisely derive expressions for the buoyancy and drag parameters of the momentum model, exactly integrate the model equations and determine solutions for bubbles and for spikes in both early-time and late-time regimes. In particular, we focus on the general situation in which the instability is driven by an acceleration having power-law time dependence. Our analysis provides extensive benchmarks for future research.
Publisher: Springer Science and Business Media LLC
Date: 18-06-2022
DOI: 10.1007/S42452-022-05000-4
Abstract: Interfaces and interfacial mixing are omnipresent in fluids, plasmas, materials in vastly different environments. A thorough understanding of their fundamentals is essential in many areas of science, mathematics, and technology. This work focuses on the classical problem of stability of a phase boundary that is a subject to fluxes of heat and mass across it for non-ideal thermally conducting fluids. We develop a rigorous theory resolving challenges not addressed before, including boundary conditions for thermal heat flux, structure of perturbation waves, and dependence of waves coupling on system parameters in a broad range of conditions. We discover the novel class of fluid instabilities in the three regimes—advection, diffusion, and low Mach—with properties that were never earlier discussed and that are defined by the interplay of the thermal heat flux, thermal conductivity and destabilizing acceleration with the inertial stabilization. We reveal the parameter controlling transitions between the regimes through varying the initial conditions. We find that the interface stability is set primarily by the macroscopic inertial mechanism balancing the destabilizing acceleration. The thermal heat flux and the microscopic thermodynamics create vortical fields in the bulk. By linking micro to macro scales, the interface is the place where balances are achieved. This work yields the general theory of interface dynamics in a broad range of conditions. The interplay is explored of inertial stabilization, destabilizing acceleration, thermal conductivity and heat flux. We discover that interface is the place where balances are achieved through linking micro to macro scales.
Publisher: American Physical Society (APS)
Date: 26-07-2022
Publisher: IOP Publishing
Date: 06-2021
Publisher: AIP Publishing
Date: 09-2021
DOI: 10.1063/5.0059898
Abstract: Three-dimensional Rayleigh–Taylor instability (RTI) with the time-varying acceleration in a finite domain is investigated in a systematic framework. The acceleration magnitude follows a power law in time with an exponent greater than −2. Applying the group theory, the instabilities are demonstrated considering the irreducible representations for observable periodic structures with a square symmetry in the plane normal to the acceleration. We derive the dynamical system and illustrate the universal form of the solutions in the linear and nonlinear regimes. The scale-dependent dynamics are shown to be single scale and multiscale in the two regimes, respectively. For the nonlinear regime solutions, fundamental scales are derived bridging the solutions in the finite- and infinite-sized domains. Special solutions for bubbles and spikes are identified from a one-parameter family of solutions. The effect of domain confinement is that the velocity and curvature decreases and shear increases as the domain size is reduced. The theory provides predictions for the flow field and demonstrates the interfacial behavior of RTI. Our results are in good agreement with the prior studies and also provide new benchmarks for experiments and simulations.
Publisher: AIP Publishing
Date: 09-2022
DOI: 10.1063/5.0119659
Abstract: Interfaces and mixing, and their non-equilibrium dynamics, govern a broad range of phenomena in nature and technology at astrophysical and at molecular scales. Supernovae and planetary convection, turbulence and turbulent mixing, combustion and chemistry-driven fluids, purification of water, and nanofabrication are a few ex les. Addressing the societal challenges posed by alternative energy sources and the efficient use of nonrenewable resources requires an improved understanding of interfaces and mixing. Non-equilibrium dynamics of interfaces and interfacial mixing couples microscopic to macroscopic scales, and is a challenge to study in theory, experiments, and simulations. This special topic explores and assesses the state of the art in the non-equilibrium of interfaces and interfacial mixing, and charts new research directions in this actively developing area.
Location: Russian Federation
Location: No location found
Start Date: 2023
End Date: 12-2024
Amount: $660,000.00
Funder: Australian Research Council
View Funded Activity